The present invention generally relates to control of the power consumption of a storage system.
A storage system generally provides a host computer with a storage area of a storage device. The host computer writes data to the storage area provided by the storage system and read data that are stored in the storage area. Recently, because the volume of data handled by storage systems has increased, storage systems have come to comprise a greater number of storage devices. However, when the number of storage devices provided by a storage system is large, the power consumed by the storage system is also large and, therefore, the costs of running the storage system increase.
This problem includes technology disclosed in Japanese Application Laid Open No. 2005-157710, for example. According to Japanese Application Laid Open No. 2005-157710, by permitting the operation of storage devices undergoing data access such as data writing or reading and halting storage devices that are not undergoing data access, the power consumed by the storage system is reduced.
The abovementioned control of the power consumption is implemented as a result of the storage system itself monitoring whether data access is being performed with respect to storage devices that the storage system itself comprises. For example, the storage system turns OFF the power of storage devices for which there has been no data access for a predetermined period and turns ON the power of storage devices which are the subject of data access when data access occurs.
However, using this method, the following problems arise. That is, it normally takes a little while before the storage device can be accessed after the power of the storage device is turned ON. For example, in cases where a hard disk drive (HDD) is utilized as a storage device, because so-called ‘spin-up’ during which the speed of the hard disk is increased until a speed permitting access is reached after the power of the HDD is turned ON, a time corresponding to the spin-up time is required until access is possible. Therefore, when data access occurs, the storage device cannot be accessed directly even when the power of the storage device which is the subject of this data access is turned ON.
This fact is considered to be a problem particularly when a fault such as one that prevents access to data in a database (‘DB’ hereinbelow) occurs and the DB is restored from the faulty state.
In other words, although an early restore of the DB from the fault is desirable in cases where the fault above occurs, storage devices (‘restore use storage device’ hereinbelow) in which data that are used for a restore (‘restore use data’, hereinbelow) are stored normally have a low access frequency. Therefore, in cases where the above technology is utilized whereby the power of the storage device is turned ON when the storage device is to undergo data access, the power of the restore use storage device is then often turned OFF. For this reason, because, in order to restore the DB at an early stage from the faulty state, the restore use data cannot be read directly from the restore use storage device irrespective of the need to read the restore use data as early as possible, the restore takes a long time.